THE MISUNDERSTOOD BEVERAGE: MILK

The greatest drink of all time. But Bonde, "we're the only species to drink the milk of another animal, so we shouldn't do it." Can anybody spot the logical fallacy at play here? If you said hasty generalization you would be correct. This is a very common one. Aside from that statement being factually inaccurate (feral cats, gulls, and other seabirds have been documented drinking milk from nursing elephant seals frequently), you can't draw that conclusion (humans shouldn't drink cow's milk) from the (false) premise that humans are the only species to drink the milk of another species. Humans are the only species to wear clothes, so therefore we shouldn't wear clothes. See how silly? Insert anything humans are the only species to do and have at it with the hasty generalizations. 

Milk (and dairy in general) get a bad wrap. I'm here to stick up for them 1. because I don't stand for bullying, and 2. because we're very ignorant to the nature of milk, it's misunderstood. I was going to cover many facets of milk here but have decided that in order to save time I'll break it up. Starting with defining milk, and then discussing lactose intolerance and lactose sensitivity since those are at the top of the misunderstood list. Let's dive into the current literature on milk and see what the science has to say about how it interacts with our bodies at the cellular level. So, put those biases aside, grab a glass of milk, and enjoy.

What is milk?

Let's start simple: milk comes in many forms, but today we'll just be looking at cow's (Bos taurus) milk, or, cattle milk. We will save non-cattle milk (goat, sheep, camel, buffalo, etc.) for another time. So what is it? A delicious white beverage. Milk is mostly water (~85-87% to be precise), the other ~13-15% are what you would call "solids" comprised of macromolecules:

2.9-3.5% Protein

3.8-5.5% Fat

5% Carbohydrates

(5)

There is a whole field of science referred to as "-omics." In this instance we are referencing data from metabolomic studies on milk which concerns the comprehensive characterization of large numbers of small molecule metabolites. Over the past 10 years we've seen numerous metabolomic studies that have identified 93 bovine milk metabolites that stem from these solids including amino acids, short peptides, carbohydrates, lipids, vitamins, nucleotides, and enzyme cofactors. Needless to say, we have a pretty good idea of what's in cow's milk. Not so scary after all.

Dairy allergies & lactose intolerance

Now, I feel that 99% of the time I bring up milk or dairy in conversation, people say they're lactose intolerant. I get it, It's super trendy. However, lactose intolerance is a very misunderstood allergy. Let's take a quick quiz on lactose.

1. Lactose is:

A. a protein

B. a bioactive compound found in dairy

C. An enzyme 

D. A milk sugar

2. True or false: Lactose intolerance and lactose sensitivity are the same

A. True

B. False

3. True or false: There is no treatment for lactose intolerance

A. True

B. False

4. True or false: Lactase deficiency itself indicates lactose intolerance

A. True

B. False

Good job—keep those answers in mind as we continue our chat. Lactose is a disaccharide (two sugar molecule) comprised of glucose and galactose. The hydrolysis (breaking down) of lactose into glucose and galactose (two, monosaccharides) requires lactase, an enzyme that people with lactose intolerance are usually deficient in. Lack of this enzyme can cause GI distress. I italicized can because the distress may result from other issues. It's well documented that lactase deficiency itself does not indicate lactose intolerance (6,12,13). Lactose is better tolerated (in terms of digestibility) when lower doses are consumed through out the day as opposed to all at once. But that goes for most things. Individuals with intolerance or sensitivity (meaning some deficiency in lactase) normally don't experience GI issues if consuming between 15g - 20g or less of lactose (~10oz of milk) especially when consumed with other foods (8,13).

So, all of this to say that we previously defined/diagnosed lactose intolerance as a deficiency in the lactase enzyme but have since realized that some lactase-deficient individuals have no adverse GI reaction to dairy and some individuals with no lactase-deficiency do have adverse GI reactions to dairy (6, 8, 12, 13). And even more interestingly, individuals who were lactase-deficient in many instances still had GI issues when drinking lactose free milk... (fun fact: they make dairy products lactose free by adding the lactase enzyme. That's it. Simple.) So, all of this made us want to keep digging. We eventually brought gut microbiome into play of course, as the microbiome is everything in research now as it relates to human health, and, arguably, rightfully so. But there's another recent discovery that has raised many interesting points with regard to diary allergies. And it all starts with the type of dairy cow you're dealing with. 

Types of cow

Not all milk is the same... Because not all cows are the same. The type of milk and metabolites you find in the end product depends on the breed of cow and environment (5). There are Holstein, Jersey, Guernsey, Ayrshire, and a lot more, but these are the major contributors to our dairy market. There's one of the bunch that we're particularly interested in. Any guesses? If you said Jersey, you're wrong, it's Guernsey. But why? Casein-a2, that's why. 

Casein-a1 vs casein-a2

I'm going to limit myself on character count here or else I'll end up with 30 pages on casein and nobody wants to read that. Casein is a phosphoprotein (it contains the amino acid phosphoserine) and is found in milk (2,6,13). Instead of walking through a complicated chain of reactions, enzymes, and biological processes, I am just going to use this diagram put together by Fransson and Lönnerdal that show the components of milk as it's "fractionated" by centrifuge (really fast spinning machine).

See, all milk contains these "macro" components. But the a1 and a2 casein proteins differ based on cow type. This is where we begin to care about the casein-a1 vs casein-a2 delineation. See A1 and A2 can be distinguished by the presence of Histidine (His) in A1 or proline (Pro) in A2. You don't have to know what that means, what's important is this: "Although His within A1 is susceptible to proteolytic cleavage, Pro within A2 is not. Thus, A1s have the potential to release short b-casomorphin (BCM) opioid peptides, including BCM-7, during gastrointestinal digestion" (2,3,4). That's HUGE. When you read that, doesn't that make you think "OOOOOOOOOOOOHHHHHHH." Probably not. That's just me. But here's why you should react the same. See, evidence found in several studies on the modulation of gastrointestinal pro-inflammatory responses that BCM-7 can trigger digestive symptoms, such as abdominal discomfort (3,4,9,10). There seems to be a specific reaction in the GI to BCM-7 compared to the other BCM peptides (BCM-4 through BCM-11). 

And get this, BCM-7 is classfied as an exphorin because it is an exogenous opioid peptide (the same classification of morphine). BCM-7 binds to the active site of μ-opioid receptors, it is assumed that it is also capable of causing structural modifications that activate signal transduction, generating biological responses. Numerous studies show concern about its physiological activity as an opioid agonist, potential to activate type μ opioid receptor (1). These receptors are located in the Central Nervous System (CNS) and the peripheral system, throughout the gastrointestinal tract, bladder, and in the cells of the immune and endocrine system (11).

If you're asking yourself what does this all mean? That's okay. Here:

We drink cow's milk. Some people drink cow's milk and go "ow my tummy hurts." Some people drink cow's milk and are fine. Of those people that drink cow's milk and go "ow my tummy hurts", some are lactase-deficient, some are not. Some people lack the proper gut bacteria to digest milk. Some have severe reactions, some have very minor. It's all over the place.

What we've just started discovering in research is that there is this casein-a1 peptide (B-Casomorph-7) that is beginning have effects elucidated that might explain and interlink all the adverse effects experienced by those who were previously diagnosed as "lactose intolerant." It could very well be a BCM-7 intolerance subsequently meaning that it's a casein-a1 allergy and that depending on the root of the issue, individuals might be able to consume casein-a2 dairy products without and adverse GI reactions. The jury is still out.

Should I be afraid of milk?

Absolutely not, milk is just misunderstood. But hopefully less by you now. Looking back to our discussion on lactose intolerance, the verdict is still out on what exactly is at the root of one's GI discomfort when consuming dairy. The casein-a1 vs casein-a2 distinction is just one of many very interesting components to add to the mix. I buy milk from the brand a2 which you can find in almost every grocery retailer. Their cows are all A2A2 allele cows. There are some companies that have great teams of people who do their research. It looks like this:

There's all kinds of stuff I wanted to cover about trace minerals, rBST, digestibility, timing, dosing, and other fun subcomponents of milk, but we'll have to save that for another conversation. 

It's been real.

~ Bonde

References:

1. Boutrou R., Gaudichon C., Dupont D., Jardin J., Airinei G., Marsset-Baglieri A., Benamouzig R., Tomé D., Leonil J. Sequential Release of Milk Protein-Derived Bioactive Peptides in the Jejunum in Healthy Humans. Am. J. Clin. Nutr. 2013;97:1314–1323. doi: 10.3945/ajcn.112.055202.
2. Brooke-Taylor, S., Dwyer, K., Woodford, K., & Kost, N. (2017). Systematic Review of the Gastrointestinal Effects of A1 Compared with A2 β-Casein. Advances in Nutrition: An International Review Journal, 8(5), 739–748. doi:10.3945/an.116.013953 
3. B.T. O’Kennedy, 2 - Caseins, Editor(s): G.O. Phillips, P.A. Williams, In Woodhead Publishing Series in Food Science, Technology and Nutrition, Handbook of Food Proteins, Woodhead Publishing, 2011, Pages 13-29, ISBN 9781845697587, https://doi.org/10.1533/9780857093639.13.
4. de Vasconcelos, M.L.; Oliveira, L.M.F.S.; Hill, J.P.; Vidal, A.M.C. Difficulties in Establishing the Adverse Effects of β-Casomorphin-7 Released from β-Casein Variants—A Review. Foods 2023, 12, 3151. https://doi.org/10.3390/foods12173151
5. Foroutan, A., Guo, A. C., Vazquez-Fresno, R., Lipfert, M., Zhang, L., Zheng, J., … Wishart, D. S. (2019). Chemical Composition of Commercial Cow’s Milk. Journal of Agricultural and Food Chemistry. doi:10.1021/acs.jafc.9b00204
6. Forsgård RA. Lactose digestion in humans: intestinal lactase appears to be constitutive whereas the colonic microbiome is adaptable. Am J Clin Nutr. 2019 Aug 1;110(2):273-279. doi: 10.1093/ajcn/nqz104. PMID: 31175813; PMCID: PMC6669050.
7. Fransson GB, Lönnerdal B. Distribution of trace elements and minerals in human and cow's milk. Pediatr Res. 1983 Nov;17(11):912-5. doi: 10.1203/00006450-198311000-00015. PMID: 6646903.
8. Hertzler SR, Savaiano DA. Colonic adaptation to daily lactose feeding in lactose maldigesters reduces lactose intolerance. Am J Clin Nutr. 1996;64:232-6.
9. Kuellenberg de Gaudry D, Lohner S, Bischoff K, Schmucker C, Hoerrlein S, Roeger C, Schwingshackl L, Meerpohl JJ. A1- and A2 beta-casein on health-related outcomes: a scoping review of animal studies. Eur J Nutr. 2022 Feb;61(1):1-21. doi: 10.1007/s00394-021-02551-x. Epub 2021 Jun 1. PMID: 34075432; PMCID: PMC8783860.
10. Roy D, Ye A, Moughan PJ, Singh H. Composition, Structure, and Digestive Dynamics of Milk From Different Species-A Review. Front Nutr. 2020 Oct 6;7:577759. doi: 10.3389/fnut.2020.577759. PMID: 33123547; PMCID: PMC7573072.
11. Sebely P., Woodford K., Kukuljan S., Ho S. Milk Intolerance, Beta-Casein and Lactose. Nutrients. 2015;7:7285–7297. doi: 10.3390/nu7095339.
12. Shaukat, A. (2010). Systematic Review: Effective Management Strategies for Lactose Intolerance. Annals of Internal Medicine, 152(12), 797. doi:10.7326/0003-4819-152-12-201006150-00241
13. Suarez FL, Adshead J, Furne JK, Levitt MD. Lactose maldigestion is not an impediment to the intake of 1500 mg calcium daily as dairy products. Am J Clin Nutr. 1998;68:1118-22.